1. Field of the Invention
The invention relates generally to batteries and particularly a battery pack including an electronic power saver circuit for an extended service life.
2. Description of Related Art
Preferred uses for electrical and electronic type equipment are evolving more and more into those which are typically referred to as "portable" uses. Much of today's electronic equipment includes portable power sources. Portable power sources may be, for example, solar power cells. The most conventional type of portable power sources for a majority of portable electric and electronic type utilization devices are batteries.
Batteries are classifiable broadly into non-rechargeable or expendable and rechargeable battery types. In each of these two categories there are batteries which differ by electrical characteristics, such as their nominal operating voltage, and by physical characteristics, such as their size, for example. In addition, batteries do not have a completely constant voltage output over the span of a discharge cycle. Depending on the type of battery involved, certain characteristics, such as charge-related voltage changes occur as the respective batteries experience a steady power drain over a single discharge cycle. Certain batteries, such as NiCad batteries, exhibit a more constant voltage output over a substantial portion of the discharge cycle than, for example, lithium type batteries.
For an electronic device to use the power of the battery over the battery's full discharge cycle, the minimum supply voltage of the battery must exceed the supply voltage requirements of the device over the entire discharge cycle of the battery. Batteries typically are rated at such a minimum voltage level, such that during the life cycle of a battery, the output voltage of the battery exceeds the nominal, rated voltage level.
Some electronic circuits of electronic devices can accept the excess voltage output by the battery without a problem. The circuits of other devices need to be protected from voltages which exceed a certain design voltage by a percentage of the nominal voltage, such as, for example, ten percent of the rated voltage. A voltage regulating circuit is consequently interposed between the power terminals of an electronic device and the particular circuit elements to be protected from an overvoltage.
An exchange of batteries in an electronic device, involving the substitution of a different type of battery, though of the same nominal voltage rating, may change the impedance of the power train and affect the operation of the circuit, even in the presence of protection circuits. Thus, typically, devices are not only designed for certain supply voltage levels, but are also restricted to the use of certain types of batteries.
Lithium type batteries are particularly distinctive in their characteristic life cycle voltage output performance, in that the voltage output of lithium type batteries varies over a single discharge cycle more than for example nickel-cadmium type batteries, the latter at a relatively constant voltage throughout most of their discharge cycle and drop off relatively sharply only when substantially discharged. While there are advantages to using lithium type batteries, the relatively wide voltage swing with respect to other type batteries over a discharge cycle of the lithium batteries presents designers with greater problems in controlling the excess available power caused by the initially greater available voltage. These problems have caused designers to shy away from specifying lithium type batteries for certain applications in which tight voltage controls are required.
Those electronic devices which include voltage protection circuits may cause higher power batteries to appear as less efficient power choices. If, for example, the protection circuits are dissipative power regulating circuits, a substantial part of the excess power may be dissipated or slowly drained by the protection circuits in effecting regulation of the supply voltage. The power drainage can often significantly diminish the life cycle or discharge cycle of the respective battery, making the battery appear to be less efficient than a comparable battery requiring less regulation over its discharge cycle.
Switching type regulators are more efficient in effecting regulation of the input voltage to a device. However, a battery supplier, for example, has no control over the type of regulator that is going to be used for a particular device to be powered by one of the supplied batteries. Hence, lithium type batteries cannot readily be taken as replacements for similarly rated batteries, in that the economic value of the battery to the consumer may be substantially diminished because of the existence of a dissipative voltage regulator circuit in a particular electronic device. If such batteries are, nevertheless, used as a replacement device, the image of the lithium batteries as a useful product may be affected detrimentally.